Method of producing hollow articles by deep drawing and press for effecting same

ABSTRACT

A press for manufacturing hollow articles by deep drawing comprising a high pressure vessel (1) accommodating a die (3) with a punch (4). A blank (14) is accommodated in an annular high pressure chamber (16) communicating with a high pressure chamber (19) of an intensifier (20). The press also comprises a device (27) for regulating pressure in the annular chamber to control pressure acting upon the peripheral portion of a blank in accordance with a preset law, an appliance (39) for setting pressure in the annular chamber is made in the form of a tracer whose profile is equidistant with the curve characterizing the alteration of pressure in the annular chamber (16).

BACKGROUND OF THE INVENTION

The present invention relates to metal working, and more particularly,to a method of producing hollow articles by deep drawing and a press foreffecting same.

A better quality of hollow articles produced by deep drawing along withthe provision of higly efficient equipment is quite essential wheredrawing of articles is effected with radial head pressure acting on theflanged portion of a blank.

There is known in the art a method of deep drawing of sheet metalswherein rigid pushers are used to act on the peripheral part of theblank in a manner to create radial head pressure effecting the flangedpart of the blank (USSR Inventor's Certificate No. 419,279, published inDiscoveries, Inventions, Industrial Designs and Trade Marks Bulletin No.10, 1974). In the process of drawing, the rigid pushers interact withthe blank through their narrow sections which causes uneven distributionof head pressure over the peripheral portion of the blank. This, inturn, makes it impossible to increase the drawing coefficient K, whichis determined by the relation of the blank radius R_(i) to the punchradius R_(o). In addition, the method described above fails to provideradial head pressure required to action the peripheral part of the blankin the drawing direction. As a result, the articles thus produced sufferfrom poor quality.

There is also known in the art a method of producing hollow articles bydeep drawing, which resides in that the central portion of a blankpositioned on a die is hermetically separated from the peripheralportion of the same blank, whereupon a high-pressure fluid is used toact upon the butt end of the blank peripheral portion, with the blankbeing drawn through the agency of a rigid punch (U.S. Pat. No.3,495,433; cl. 72-347, published 1977). In the process of drawing, thepressure applied to the peripheral portion of the blank is brought down.This occurs due to a decrease in the diameter of the blank peripheralportion. However, at the initial stage of drawing the pressure tends tocrowd the metal into a shape without the punch participation, whichresults in an undesirable dome-formation in the central portion of theblank and, consequently, in a higher percentage of defective products.

The prior art teaches a press for the manufacture of hollow articles bydeep drawing, which comprises a high-pressure vessel accommodating a diewith a punch in rigid connection with a piston of a punch-actuatinghydraulic cylinder, and a clamp formed with a collar provided to ensurehermetic separation of the blank central portion from its peripheralportion. The clamp is located opposite a drawing rib of the die whoseend surface forms, together with the end surface of the clamp, ahigh-pressure annular chamber which accommodates the blank peripheralportion and communicates with a high-pressure chamber of an intensifier(U.S. Pat. No. 3,495,433; Cl. 72-347, published 1977).

The die is formed with a plurality of vertical grooves intended tocommunicate the annular high-pressure chamber with a pressure source. Inits upper part, the die is fitted with a channel intended to communicatethe die cavity through a return valve with the cylinder chamber intowhich a fluid, delivered along a line, is discharged. The cylinder isbrought in contact with the high-pressure vessel to form an annularchamber wherein hydrostatic pressure of fluid is created to act on theperipheral portion of the sheet metal blank in the process of drawing.

This high hydrostatic pressure is not adjusted in the process ofdrawing, its value at the beginning and at the end of the drawingoperation being very much in excess of a specified value. As a result,the formation of the peripheral part of the blank is effectedspontaneously at the initial stage of drawing; thin-walled articles tendto wrinkle and thick-walled articles develop dents or hollows on theirsurfaces at the end of the drawing process.

SUMMARY OF THE INVENTION

The invention has as its aim the provision of a method and a press forproducing hollow articles by deep drawing, wherein an alteration ofpressure acting on the peripheral portion of a blank in the process ofdrawing in accordance with a given law will make it possible to improvethe quality of articles being drawn.

This aim is attained in a method of producing hollow articles by deepdrawing, consisting in that the central portion of a blank positioned ona die is hermetically separated from the blank peripheral portion, thebutt end of the blank peripheral portion is acted upon by ahigh-pressure fluid, and the drawing of the blank is effected by meansof a rigid punch, wherein, according to the invention, the pressure q isaltered in accordance with the following law: ##EQU1## where β is thecoefficient accounting for the influence of an average main stress ofthe blank material;

σ is the yield stress of the blank material;

R_(i) is the blank running radius;

R_(o) is the punch radius;

t is the wall-thickness of a finished product;

σ is the stress on the interior edge of the peripheral portion of ablank.

The aim of the invention is also accomplished by the provision of apress for carrying into effect the method of the invention, comprising ahigh-pressure vessel accommodating a die with a punch in rigidconnection with a piston of a punch-actuating hydraulic cylinder, and aclamp formed with a collar for hermetic separation of the centralportion of a blank from its peripheral portion and positioned opposite adrawing rib of the die whose end surface forms, together with the endsurface of the clamp and with the inner surface of the high-pressurevessel, an annular high-pressure chamber which accommodates theperipheral portion of the blank and communicates with a high-pressurechamber of an intensifier according to the invention, there is provideda pressure regulator arranged in the annular chamber and incorporating ahydraulic cylinder with a piston, the piston cavity of which is broughtin communication with a rod cavity of the punch-actuating hydrauliccylinder, an appliance for setting pressure in the annular high-pressurechamber, altered in accordance with a specified law, said appliancebeing fixed on the piston rod, a regulator of pressure created in thehigh-pressure chamber of the intensifier and acting on the peripheralportion of the blank, said pressure regulator having its sensitiveelement in contact with the pressure setting appliance.

It is advantageous for the press to be provided with a means foradjusting the travelling speed of the pressure setting appliancerelative to the punch having a hydraulic motor and a hydraulic pump withan adjustable rate of delivery, the former and the latter being mountedon a common shaft and respectively brought in communication with the rodand piston cavities of the punch-actuating hydraulic cylinder and of ahydraulic cylinder for actuating the pressure setting appliance.

It is preferable that the pressure setting appliance be provided in theform of a tracer with the profile thereof being equidistant with thecurve characterizing the alteration of pressure in the annularhigh-pressure chamber.

With the method of the invention it becomes feasible to control, inaccordance with a preset law, a fluid high pressure acting on theperipheral portion of a blank in the direction of its drawing. Thiseliminates the possibility for self-drawing of the blank withoutparticipation of the punch, effected only under the action of the radialhydrostatic head created by the high-pressure fluid. In other words, anyuncontrolled operation in the formation of the blank bottom portion isexcepted to thereby allow better quality of the finished product.

Furthermore, the method of the invention allows for the application offluid pressure to be used at optimal values at each stage of the drawingoperation, making it possible to control magnitudes of stresses actingin the drawn portion of the blank or, in other words, to gain controlover the quality of finished product. In addition, the method of theinvention is carried out in a manner permitting the finished product tobe prevented from "shooting" into the die cavity at the end of thedrawing process, which causes wrinkling of the thin-walled products andformation of dents on the surface of thick-walled articles. In otherwords, it becomes possible to ensure high quality of the product beingdrawn.

The fact that the press of the invention is equipped with a device forregulating high pressure of fluid, acting on the peripheral part of theblank in the process of its drawing, makes it possible to improve thequality of finished product. Owing to the fact that the high-pressureregulating assembly is equipped with a removable tracer, whose contouris equidistant with the curve ##EQU2## optimal fluid pressures can beapplied to the peripheral portion of the blank. This, in turn, willpreclude spontaneous crowding of the blank flange without participationof the punch at the initial stage of the drawing operation, as well asprevent the finished product from being "shot" into the die cavity atthe end of the drawing process. Thus, good conditions are created topermit appropriate formation of the peripheral portion of the blank andto prevent wrinkling or the formation of dents or scratches on thefinished product.

The provision of the speed regulator intended to control the travellingspeed of the tracer, functioning to preset a law of alteration of highfluid pressure acting on the blank peripheral portion relative to thepunch, makes it possible to improve the quality of technologicallysimilar articles, that is of those manufactured from one and the samematerial, having the same drawing coefficient K, through the use of oneand the same tracer.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 is a hydromechanical diagramme of a press for the production ofhollow articles by deep drawing, according to the invention;

FIG. 2 shows an intermediate stage of drawing a hollow article from aflat blank with radial hydrostatic head pressure being applied to theblank peripheral portion, and a chart depicting an alteration ofpressure corresponding to the profile of a tracer intended for setting alaw of the fluid pressure alteration due to take place in the directionof drawing, according to the invention.

Referring now to the drawings, and to FIG. 1 in particular, there isshown therein a press for carrying into dffect the method of theinvention for producing hollow articles by deep drawing, which comprisesa high-pressure vessel 1 mounted on a table 2. The vessel 1 accommodatesa die 3 and a punch 4 which is rigidly connected with a piston 5 of apunch-actuating hydraulic cylinder 6. The punch 4 is positioned in anaxial opening of a clamp 7. The punch-actuating hydraulic cylinder 6 islocated in a rod 8 of a hydraulic cylinder 9 for actuating a slidingcrosspiece 10. The crosspiece 10 is slidable along guides 11 and isintended for moving the clamp 7. There is also provided a stationarycrosspiece 12 which is rigidly fixed on the guides 11 and accommodatesthe hydraulic cylinder 9.

The clamp 7 has its end face, presented to the die 3, formed with anannular collar 13 intended for hermetic separation of the centralportion of a blank 14 from its peripheral portion disposed opposite adrawing rib 15 of the die 3.

The end surface of the die 3 forms, together with the end surface of theclamp 7 and the interior face of the high-pressure vessel 1, an annularhigh-pressure chamber 16. The vessel 1 has a pressed-on shell 17. Thechamber 16 communicates through a channel 18 with a high-pressurechamber 19 of an intensifier 20. The intensifier 20 has its low-pressurechamber 21 brought in communication through a pipeline 22 with apressure regulator 23.

The chamber 19 communicates with a return valve 24 for blowing-throughthe annular chamber 16. The valve 24 has its input brought incommunication with a rod cavity 25 of the intensifier 20 and with ahydraulic distributor 26.

The press of the invention also comprises a device 27 for regulatingpressure in the high-pressure chamber of the intensifier 20 which deviceincorporates a hydraulic cylinder 28 with a piston 29. A piston cavity30 of the hydraulic cylinder 28 communicates through a hydraulicdistributor 31 and a pipeline 32 with a rod cavity 33 of thepunch-actuating hydraulic cylinder 6. A rod cavity 34 of the hydrauliccylinder 28 communicates through a pipeline 35, the distributor 31, thepipeline 32 and a distributor 36 with a tank 37. Fixed on a rod 38 ofthe hydraulic cylinder 28 is an appliance 39 for setting pressure in theannular high-pressure chamber 16, which pressure is subjected toalteration in accordance with a prescribed law. A sensitive element 40of the pressure regulator 23 is brought in contact with the profiledsurface of the pressure setting appliance 39.

The press is also provided with an appliance for regulating thetravelling speed of the pressure setting appliance 39 relative to thepunch 4. This speed regulator makes it possible to manufacture articlesfrom one and the same material, having the same drawing coefficient K,but varying in length and diameter, without replacing the pressuresetting appliance 39. The speed regulator includes a hydraulic motor 41and a hydraulic pump 42 with an adjustable rate of delivery, the formerand the latter being mounted on a common shaft 43. The hydraulic motor41 is brought in communication through the hydraulic distributor 36,pipeline 32 with the rod cavity 33 of the hydraulic cylinder 6; and thehydraulic pump 42 communicates through a pipeline 44 with the pistoncavity 30 of the hydraulic cylinder 28. There are provided a valve 45and a pressure gauge 46, which are intended for setting the hydraulicpump 42 to a requisite pressure.

The intensifier 20 is operated by means of a hydraulic pump 47delivering oil along pipelines 48, 49, 50. The finished product iswithdrawn from the die 3 by means of a pusher 51 whose movement issynchronized with that of the sliding crosspiece 10. The pusher 51 isformed with an axial passage along which the oil under pressure isdelivered to the die cavity. The oil pressure in this cavity is requiredto enable the drawing of articles from materials having low plasticity.There is provided a valve 52 intended to remove the air from the chamber16 prior to drawing, which valve communicates through a passage 53 withthe chamber 16.

The distributor 36, connected to a discharge line 54, is brought incommunication with a piston cavity 55 of the hydraulic cylinder 6through a pipeline 56.

In the preferred embodiment of the invention, the pressure settingappliance 39 is provided in the form of a removable tracer with theprofile thereof being equidistant to the curve characterizing thealteration of pressure in the annular high-pressure chamber 16. Forbetter understanding of the invention, there is shown in the right-handpart of FIG. 2 a chart depicting an alteration of pressure correspondingto the tracer contour and constructed in coordinates where the abscissais the pressure q, and the ordinate is the value h of the working strokeof the punch 4. Shown in the left-hand part of FIG. 2 is an intermediatestage of the blank 14 with the indication of pressure q acting on theperipheral portion of the blank 14.

The scale along the Y-axis is selected with regard to the coefficient K₁of proportionality between the travelling speeds of the pistons 5(FIG. 1) and 29. The tracer contour has three characteristic pointsq_(o) (FIG. 2), q_(max) and q₁. The point q_(o) is given to determinethe value of pressure applied to the peripheral portion of the blank 14prior to the working stroke of the punch. Here the pressure value isselected to be below that at which occurs self-drawing of the blank 14,resulting in swelling of the blank central portion. The point q_(max) isgiven to characterize the value of pressure applied to the peripheralportion of the blank 14 on attaining the critical drawing coefficient Kcharacterized by maximum stresses acting on the inner edge of the flangeof the blank 14 being drawn. The point q₁ determines the pressure atwhich it becomes possible to prevent "the shooting" of the finishedproduct into the cavity of the die 3 at the end of drawing.

The press according to the invention for producing hollow articles bydeep drawing operates in the following manner.

Originally, the clamp 7 (FIG. 1) and the sliding crosspiece 10 with thepiston of the hydraulic cylinder 9 are found in the extreme upperposition. The clamp 7 is brought out of the high-pressure vessel 1. Thepiston 5 with the punch 4, as well as the rod 38 with the tracer 39,occupy extreme upper positions. The piston of the intensifier 20occupies an extreme right-hand position, the valve 52 is open, and thepusher 51 occupies extreme lower position.

The blank 14 is introduced into the open cavity of the high-pressurevessel 1 and is then mounted on the die 3. With the press put inoperation, the press control hydraulic circuit (not shown in FIG. 1)operates to enable downward movement of the piston of the hydrauliccylinder 9 with the crosspiece 10 and clamp 7. As the clamp 7 goes down,it enters the cavity of the high-pressure vessel 1. The annular collar13 of the clamp 7 is brought in contact with the blank 14, therebyproviding for reliable hermetic separation of the central portion of theblank 14 from its peripheral portion. This results in the formation ofthe high-pressure chamber 16. Thereafter, the hydraulic distributor 26occupies position 11 at which the pipeline 48 is brought incommunication with the pipeline 50, and the pipeline 49 with an outletline. The fluid delivered by the pump 47 is passed through the valve 24to the high-pressure chamber 19 of the intensifier 20 and thence alongthe channel 18 to the chamber 16, wherein is located the peripheralportion of the blank 14, thus forcing out the air therefrom through theopen valve 52.

After a certain period of time, preset by a time relay (not shown inFIG. 1), the valve 52 is closed, the distributor 26 occupyingposition 1. At this moment, the pipeline 48 is brought in communicationwith the pipeline 49, and the pipeline 50 with an outlet line, whereuponthe fluid delivered by the pump 47 is passed to the piston cavity 21 ofthe intensifier 20.

As the piston of the intensifier 20 travels in the left-hand direction,it creates high pressure q of the fluid disposed in the chamber 16,which pressure acts on the peripheral portion of the blank 14. The valueof this pressure is determined by the position of the tracer and of thesensitive element 40 of the pressure regulator 23, and does not exceedthe pressure permitting self-drawing of the blank 14.

Then ensues the process of drawing a hollow article. The distributor 36occupies position II at which the pipeline 54 is brought incommunication with the pipeline 56, and the pipeline 32 with thehydraulic motor 41. The distributor 31 occupies position 1 at which thepipeline 35 is disconnected from the pipeline 32 and brought incommunication with an outlet line. As a result, the piston cavity 55 ofthe hydraulic cylinder 6 is brought in communication with the pipeline54. The fluid from the rod cavity 33 of the hydraulic cylinder 6 ispassed through the distributor 36 to the hydraulic motor 41 which setsin rotation the shaft 43 of the pump 42 with an adjustable rate ofdelivery. The pump 42 is brought in communication through the pipeline44 with the piston cavity 30 of the hydraulic cylinder 28. From the rodcavity 34 of the hydraulic cylinder 28, the fluid is passed through thedistributor 31 to an outlet line. The rod 38 of the piston 29 movesdownward together with the tracer. On interacting with the sensitiveelement 40 of the pressure regulator 23, the tracer functions to alterthe fluid pressure in the chamber 16, acting on the peripheral portionof the blank 14 in accordance with the following law: ##EQU3## where βis the coefficient accountant for the influence of an average mainstress of the blank material;

σ is the yield stress of the blank material;

R_(i) is the blank running radius;

R_(o) is the punch radius;

t is the wall-thickness of a finished product;

σ₁ is the stress acting on the interior edge of the peripheral portionof a blank.

The pressure alteration law is determined by the tracer contour andallows for optimal pressure value to be attained at each stage of thedrawing operation.

By adjusting the delivery rate of the pump 42, functioning to deliveroil to the piston cavity 30 of the hydraulic cylinder 28, it becomespossible to control relative speed of travelling of the punch 4 and thatof the rod 38 carrying the pressure setter 39. By virtue of this factorthe tracer contour is permitted to be either "stretched" or "contracted"along the axis h (FIG. 2) at constant coordinate of the point q_(o)given to determine initial pressure acting on the peripheral portion ofthe blank 14 at the initial stage of drawing. Thus, the press can besuccessfully used for the production of technologically similararticles, i.e. of the articles made of one and the same material, havingthe same drawing coefficient K, and making use of one and the sametracer.

Towards the end of the operating cycle, with the drawing operationcompleted, the distributor 26 is shifted into position II, whereuponhigh fluid pressure q₁ in the chamber 16 is brought down to the value ofpressure gained by the pump 47, with the piston of the intensifier 20being returned to its original position. Then, the sliding crosspiece 10is lifted together with the clamp 7 to upper position. The distributor36 is shifted into position 1 at which the pipeline 54 is brought incommunication with the pipeline 32, and the pipeline 56 with thedischarge tank 37. As this happens, the piston 5 is found in its upperoriginal position. The distributor 31 occupies position II functioningto return the piston 29 with the pressure setting appliance 39 tooriginal position.

On completion of the drawing cycle, the pusher 51 travels in the upwarddirection, thereby forcing out a finished product from the cavity of thedie 3.

INDUSTRIAL APPLICABILITY

A press for manufacturing hollow articles by deep drawing is used mainlyin the metal working industry for the fabrication of deep cylindricalcups with a wide flange or without it, from a flat or predrawn blank ofany rectangular or irregular shape (circle, oval, diamond, square).

The invention is well suited to the manufacture of shells, sleeves andprotective screens.

We claim:
 1. A press for producing hollow articles by deep drawing of ablank comprising a high-pressure vessel, a die accommodated in said highpressure vessel and having a drawing rib engageable with a blank, apunch accommodated in said high pressure vessel, a punch-actuatinghydraulic cylinder having a piston rigidly connected with said punch, aclamp formed with a collar for hermetic separation of a central portionof the blank from a peripheral portion and positioned opposite thedrawing rib of the die, the die having an end surface which forms,together with an end surface of the clamp and with an inner surface ofthe high-pressure vessel, an annular high-pressure chamber wherein ispositioned the peripheral portion of the blank, a high-pressure chamberof an intensifier communicating with said annular high-pressure chamber,a pressure regulator for controlling pressure in the annular chamber andincorporating a second hydraulic cylinder and a second piston whosecavity is brought in communication with a rod cavity of thepunch-actuating hydraulic cylinder, an appliance for setting pressure inthe annular high-pressure chamber, said appliance being fixed on a rodof the second piston, and a regulator of pressure created in thehigh-pressure chamber of the intensifier and acting on the peripheralportion of the blank, said pressure regulator having a sensitive elementbrought in contact with the pressure setting appliance whereby thepressure in the annular high pressure chamber is varied in accordancewith movement of said punch to thereby control the quality of the drawnblanks.
 2. A press as claimed in claim 1, characterized in that itcomprises a means for adjusting the travelling speed of the pressuresetting appliance relative to the punch having a hydraulic motor and ahydraulic pump with adjustable rate of delivery, the former and thelatter being mounted on a common shaft and brought respectively incommunication with the rod and piston cavities of the punch-actuatinghydraulic cylinder and of a hydraulic cylinder for actuating thepressure setting appliance.
 3. A press as claimed in one of claims 1 or2, characterized in that the pressure setting appliance is provided inthe form of a tracer whose profile is equidistant with the curvecharacterizing the alteration of pressure in the annular high-pressurechamber.
 4. A press as claimed in one of claims 1 or 2, wherein theappliance for setting pressure is shaped to alter pressure q inaccordance with the following: ##EQU4## where β is the coefficientaccounting for the influence of an average main stress of the blankmaterial;σ_(s) is the yield stress of the blank material; R_(i) is theblank running radius; R_(o) is the punch radius; t is the wall-thicknessof a finished product; σ₁ is the stress on the inner edge of theperipheral portion of a blank.
 5. A press as claimed in claim 3, whereinthe appliance for setting pressure is shaped to alter pressure q inaccordance with the following: ##EQU5## where β is the coefficientaccounting for the influence of an average main stress of the blankmaterial;σ_(s) is the yield stress of the blank material; R_(i) is theblank running radius; R_(o) is the punch radius; t is the wall-thicknessof a finished product; σ₁ is the stress on the inner edge of theperipheral portion of a blank.